/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h
Computes the barycentric coordinates for a given point in a triangle, only considering the XY coordinates - simpler than the Compute versions
Vector containing the three weights a,b,c such that Point = a*A + b*B + c*C or Point = A + b*(B-A) + c*(C-A) = (1-b-c)*A + b*B + c*C
static FVector GetBaryCentric2D ( const FVector & Point, const FVector & A, const FVector & B, const FVector & C )